In the prior art, invertible ink stamps of this sort not in use or on standby typically have their impressing faces retained in contact with an ink pad to supply the impressing faces with ink, and the invertible ink stamps in service have their impressing faces turned out to get ready for impressing mark on a surface. Repeatedly impressing results in ink impregnating the ink pad being used up, and the ink pad must be replenished with ink. The ink pad fitted in a stamp casing has to be first withdrawn and then impregnated with ink dripped from an external ink source. For that purpose, an appropriate amount of the replenishment ink must be known, or otherwise, an excessive amount of the liquid ink is likely to be applied. To shoot such a trouble, an improved version of the invertible ink stamps permits a user to supply ink to the ink pad through a pipe coupled to an ink impregnated member in an upper portion of the ink pad, as known in Patent Document 1, namely, Japanese Official Gazette of Preliminary Publication of Examined Utility Model S41-19042.
In the invertible ink stamp disclosed in Patent Document 1, the ink impregnated member is supplied with ink gradually through the pipe until it is completely filled up to the maximum capacity. After that, the pipe has its inlet closed to get ready for impressing work, but a rapid temperature rise and the resultant rapid increase in the internal pressure of the pipe is prone to cause an overflow of ink from the ink impregnated member to such an extent that the ink drips from the ink stamp.